Calibre Web Epub Downloading + Calibre Wireless Device Syncing (#219)

## Summary

Adds support for browsing and downloading books from a Calibre-web
server via OPDS.
How it works
1. Configure server URL in Settings → Calibre Web URL (e.g.,
https://myserver.com:port I use Cloudflare tunnel to make my server
accessible anywhere fwiw)
2. "Calibre Library" will now show on the the home screen
3. Browse the catalog - navigate through categories like "By Newest",
"By Author", "By Series", etc.
4. Download books - select a book and press Confirm to download the EPUB
to your device
Navigation
- Up/Down - Move through entries
- Confirm - Open folder or download book
- Back - Go to parent catalog, or exit to home if at root
- Navigation entries show with > prefix, books show title and author
- Button hints update dynamically ("Open" for folders, "Download" for
books)
Technical details
- Fetches OPDS catalog from {server_url}/opds
- Parses both navigation feeds (catalog links) and acquisition feeds
(downloadable books)
- Maintains navigation history stack for back navigation
- Handles absolute paths in OPDS links correctly (e.g.,
/books/opds/navcatalog/...)
- Downloads EPUBs directly to the SD card root
Note
The server URL should be typed to include https:// if the server
requires it - HTTP→HTTPS redirects may cause SSL errors on ESP32.

## Additional Context

* I also changed the home titles to use uppercase for each word and
added a setting to change the size of the side margins

---------

Co-authored-by: Dave Allie <dave@daveallie.com>

src/activities/home/HomeActivity.h

@@ -13,12 +13,14 @@ class HomeActivity final : public Activity {
   int selectorIndex = 0;
   bool updateRequired = false;
   bool hasContinueReading = false;
+  bool hasOpdsUrl = false;
   std::string lastBookTitle;
   std::string lastBookAuthor;
   const std::function<void()> onContinueReading;
   const std::function<void()> onReaderOpen;
   const std::function<void()> onSettingsOpen;
   const std::function<void()> onFileTransferOpen;
+  const std::function<void()> onOpdsBrowserOpen;
 
   static void taskTrampoline(void* param);
   [[noreturn]] void displayTaskLoop();
@@ -28,12 +30,14 @@ class HomeActivity final : public Activity {
  public:
   explicit HomeActivity(GfxRenderer& renderer, MappedInputManager& mappedInput,
                         const std::function<void()>& onContinueReading, const std::function<void()>& onReaderOpen,
-                        const std::function<void()>& onSettingsOpen, const std::function<void()>& onFileTransferOpen)
+                        const std::function<void()>& onSettingsOpen, const std::function<void()>& onFileTransferOpen,
+                        const std::function<void()>& onOpdsBrowserOpen)
       : Activity("Home", renderer, mappedInput),
         onContinueReading(onContinueReading),
         onReaderOpen(onReaderOpen),
         onSettingsOpen(onSettingsOpen),
-        onFileTransferOpen(onFileTransferOpen) {}
+        onFileTransferOpen(onFileTransferOpen),
+        onOpdsBrowserOpen(onOpdsBrowserOpen) {}
   void onEnter() override;
   void onExit() override;
   void loop() override;